Often in the operation of industrial furnaces it is desired that heat be provided to a furnace charge such as aluminum within the furnace for heating and/or melting the charge. While the heat may be generated by a number of means, such as by electric resistance coils, it is generally more economical to generate the heat by the combustion of fuel with oxidant. Until recently, air has been the preferred oxidant because of its low cost. However, many industrial furnaces have switched or will soon switch to an oxidant having a higher oxygen concentration than that of air in order to take advantage of the improved energy efficiency and the environmental benefits attainable with such oxy-fuel combustion.
The use of combustion to generate heat for heating a charge may have a deleterious effect on the charge. Those skilled in the art have addressed this potential problem by providing a protective atmosphere over the charge surface between the furnace charge and the combustion reaction. The combustion gases are exhausted from the furnace from above the combustion reaction so as to ensure that the combustion gases stay well removed from the charge surface. One important recent development in this area is disclosed and claimed in U.S. Pat. No. 5,563,903--Jebrail et al.
While this conventional protective atmosphere heating arrangement has provided acceptable results when the height of the top surface of the charge is low relative to the burner height or when the charge is molten, there has been experienced relatively high levels of NO.sub.x generation with this system. Moreover, the fuel and oxidant consumption is relatively high and potential corrosion of refractory walls and burner parts within the furnace is a concern.
Accordingly, it is an object of this invention to provide a method for providing heat to a large volume of furnace charge using combustion with a protective atmosphere therebetween which enables the reduced generation of nitrogen oxides (NO.sub.x).
It is another object of this invention to provide a method for providing heat to a furnace charge using oxy-fuel combustion with a protective atmosphere therebetween which enables the reduced consumption of fuel and oxidant.
It is a further object of this invention to provide a method for providing heat to a furnace charge using combustion with a protective atmosphere therebetween which enables the furnace to operate with a reduced level of refractory corrosion.